Method of making a hollow mold of compacted mold forming material



May 27, 1952 L, JOHNSTON 2,598,554

' METHOD OF MAKING A HOLLOW MOLD OF COMPACTED MOLD FORMING MATERIAL Filed July 29, 1948 ATTORNEYS Patented MayV 27, 1952 METHOD OF MAKING A HOLLOW MOLD OF COIMPACTED MOLD FORMING MATERIAL Loyal L. Johnston, Zelienople, Pa., assgnor to Herman Pneumatic Machine Company, Pitts' burgh, Pa., a corporation of Pennsylvania Application July 29, 1948, Serial No. 47,532

2 Claims.

illustration the invention will be described in.

connection with the preparation of compacted sand molds in elongated generally cylindrical flasks for use in the centrifugal casting of cast iron soil pipe. Apparatus such as Will be referred to herein may, for example, be embodied in molding machines of the type disclosed in my copending application Serial No. 648,318, 110W Patent 2,449,900, issued September 21, 1948.

One method of preparing a mold for the centrifugal casting of cast iron soil pipe is to introduce loose or uncompacted mold forming material such as sand into an elongated generally cylindrical flask and compact the sand against the inner wall of the flask to form a hollow generally internally cylindrical compacted sand mold. The thus formed mold is rotated at high speed and molten iron is introduced into it to centrifugally cast lengths of pipe. Soil pipe is made in a range of standard nominal diameters, i. e., 2", 3, 4", 6" and 8". For each nominal diameter there is a specified external diameter of the pipe and, of course, the internal diameter of the mold must be such as to form the pipe to the proper external diameter. The wall thickness and internal diameter of the pipe are controlled by the quantity of molten metal introduced into the mold.

In a foundry for the centrifugal casting of cast iron soil pipe there are provided flasks of different sizes or large flasks adapted to receive inserts to form in effect flasks having different internal diameters. The sand may be compacted Within the flasks by mandrels. One method of procedure is to introduce loose sand into a flask and rotate the flask fast enough to cause the sand to cling to the inner wall of the flask and somewhat densify itself, thus forming a hole in the sand through the flask through which a mandrel may be introduced. A mandrel is then introduced and moved transversely of the axis of the flask to compact the sand against the inner wall of the rotatingask. The fiask may be oriented with its axis generally vertical when the sand is introduced and it may be oriented with its axis generally horizontal when the mandrel is introduced.

It is important that the sand molds formed within the asks be of proper density and properly shaped and surfaced fromend to end of the flask; otherwise the pipe cast in the mold may be defective. If the loose sand which is initially introduced into the flask does not substantially completely fill the iiask that sand may not be, and often is not, properly distributed along the flask, and thus the mold is likely to be imperfect adjacent one end of the flask. Hence the flask should be lled substantially full of loose sand at the beginning of the mold forming operation. However, this may entail the subsequent removal from the flask of sand initially introduced there-v into in excess of the quantity of sand required to form the mold. For example, in my said copending application there is disclosed a screw conveyor adapted to be introduced into the flask before the mandrel is introduced to remove excess sand. This is an undesirable operation because it entails the expenditure of considerable time, the employment of labor and a substantial additional initial outlay for equipment. Moreover it is wasteful of sand which in the grades required for foundry work is costly. Also, the sand withdrawn from the flask has to be 'removed, which entails additional time, labor and equipment.

Efforts to obviate the introduction of excess sand into the flask have been unsuccessful. While the quantity of sand needed for formation of a mold is known in advance, if that sand is measured before being introduced into the flask additional measuring equipment, time and labor are required. Moreover, if the required amount of said is insufficient to substantially fill the ask before the sand is compacted a defective mold may be formed, as above explained. The problem has been a vexing one and has not been solved prior to the present invention.

I have discovered that all of the disadvantages above referred to which have existed in foundry practice for many years may be obviated by proper proportioning of flask diameter in relation to the diameter of the mold to be formed in the iiask. This involves consideration of the initial volume of the uncompacted molding material, its volume when compacted and hence the difference in density between the uncompacted and compacted molding material. Consideration must be given to the relative internal diameters ,of Athe .flask and the mold to be formed in the flask.

I utilize for the formation of an elongated hollow mold of compacted molding material a fiask Whose volume is substantially equal to the volume of the uncompacted molding material required for formation of the desiredV mold'in the flask. In other words, the ask itself maybe employed to measure the loose .or un'compacted molding material, thus obviating any otherimeasuring apparatus. When my flask is filled substantially full of uncompacted molding material it contains the proper quantity of ,molding material for formation of the mold. Since the flask is filledA substantially full of uncompacted molding material the molding material is disposed against the inside of the iiask from -end to end of the flask and the formation of a proper mold is thus. assured. No mechanism such as ythe screw conveyor of myY said application is needed to remove fromthe Vflask sand; in excess of the There is no wastage of sand and .no-means'need be provided for removing excess sand.

Proper proportioningof the flask .requiresccnsideration of the relationshipbetween the -internal diameter of the flask and the internal; diameterof the mold as well `as the ratio *betweenY the-,specific gravity of the mold A.forming mat-erial when in looseor uncompacted conditionand the specific lgravity of the mold formingV material when compactedi to -for-m the mold. I -nd Vthat*.within thenormalrange of sizes. of cast iron soil pipeand especially the smaller-sizes which are :in greatest demand :ny-improved results are obtained when the internal diameter of the flask tpearsv approximately the following relation to the internal diameter of the mold4 to be formed therein (which is approximately the-same asrthe external diameter of the pipe to-be cast therein) in which a is the internal diameter ofy the flask, b is lthe-internalrdianleter of the -mold Yand isthefratio ofthe specific gravity ofi the compacted mold forming material' to the specificV gravity of the uncompacted mold formingmaterialas delivered into kthe flask before formation ofthe mold.

Itis a `rule cf thumb'which has becomestandard' inv foundries 'that 'a' cubic foot of Yrammedv or compacted sand weighs 1.00 pounds. This, of course, `is not"r always strictly' true Aas the weight cfacubic foot of compacted moldfcrmingmate-Y rial depends cnzthe precise.- grade. 'of material emiployed, thefcrceV with which it is `compacted, the amount of moisture it contains, etc. However, it is found that for'practicalfpurposes the'weight of a cubicfoot of' compacted mold forming-mateing material averages aroundi72pcunds per cubic foot and is rarely less than pounds per cubic foot or more than 80 pounds per cubic foot. For practical purposes the weight of uncompacted molding,materialmaybe considered as being between- -and`80pounds per cubic foot.

Theequationgiven above may be simplified for practical purposes if 1.4 be substituted for the ratio This leads to the equation which in all cases Which-I have .encounteredhasv proved applicable; `that isto say., if the internal diameter of the flask als-made tofbear the relationship expressed by the equation just .given to the internal diameter of the compacted mold .formed in the-flask, the laskmayl be usedto=measurethe amount of uncom-pacted-mold forming material. introducedY into it 4and that materialwhencompacted Vin accordanceY with accepted foundry practice will substantially `exactly. fcrma mold.

of the desired internal diameter. As amatter nfv fact, the variable is.notrthe .internal diameterv cf: the mold but ratherlitsrdensity since the internal diameter of the moldxis determined by, -the `extent of movement transverselyv of .its axis'of the mandrel used for .compacting the mold forming material. When the amount oflmold forming materialA employed. for making .a .mold Yis determined as I have explained abovea-nd the .moldis compacted and shaped by the .mandrel to the-desired internal diameter Yits `density willbe found to be satisfactory and will be inthe neighborhoodv of 1.4 times the .density of. .theloose or uncompacted. mold forming material. as introduced into the flask before formation of themold.

Since the internal diameter of the moldfor each.v size of soil pipeis fixed, I can, .by .application of the above formulae, determine the in ternal diameter of the 'flask which should be used for each size. If the practice .in any foundry is unusual so that. theinoldforming material is not compacted to. the extent that thespecic gravity of' the .compacted mold .forming material is in the neighborhood of 1.4 timesthe specific gravity of the uncompacted. .moldforming material, the particular `practice followed in that foundry is takeninto consideration and the proper value of is inserted into the equation. first given. above,

whereupon since the valueof-.bris giventhe value of a may be determined. In foundries.-followingnormal practice infselection and' ccmpactingofmold forming material'the second formula given above may be employed Vand-'the internal diameter of the flaskformakingacompactedmold -of predetermined internal diameter may be computed.

To illustrate the practical operation of my invention I, give below a partial tabulation of flask andmolddiameters which may be employed in connection with the centrifugal casting of soil pipe:

Ii will be seen by computation that the figures given in the above table do not exactly follow my formulae but they are so close that the differences between the gures obtained by my formulae and those given in the table are immaterial. So long as my formulae are followed within a plus or minus variation of 20% the improved results of my invention are obtained.

I shall give a specific example of application of my invention. Assume that it is desired to prepare a compacted sand mold for the centrifugal casting of soil pipe of 2" nominal diameter. I select a flask whose internal diameter is 41/2". This may be the internal diameter of the fiask itself or it may be in the internal diameter of an insert disposed within the flask. In either event the effective internal diameter of the flask so far as formation of the mold is concerned is 41/2. I dispose the flask with its axis generally vertical. With the flask thus disposed I fill it level full of molding sand of normal type and consistency for the purpose. The sand is simply poured into the upended ask and fills it up substantially to the top while the sand is in loose or uncompacted state. I then orient the flask with its axis generally horizontal and rotate it at high enough speed so that the sand, which lies against the flask throughout the entire length of rthe flask, is somewhat densified and an opening formed through it axially of the ask. I then introduce through the opening a sand compacting mandrel such as is shown in my said copending application. That mandrel may be journaled for rotation at both ends just outside the flask. While the flask continues to rotate the mandrel is moved transversely of its axis to compact the sand against the inner wall of the flask. The internal diameter of the compacted sand mold is determined by the amplitude of lateral movement of the mandrel which is controlled so that the internal diameter of the mold is 2%. It will be found that the quantity of sand determined by measuring it level full in the flask when the sand is in loose or uncompacted state is the proper amount for formation of the mold of desired density. While the density of the mold may vary within narrow limits it will be found to be eminently satisfactory for the purpose intended.

The accompanying drawing is a fragmentary axial cross-sectional View of a flask containing a hollow mold of compacted sand adapted to be rotated at high speed for the centrifugal casting of elongated hollow articles. The flask is shown at 2 and the hollow mold therein of compacted sand is shown at 3. An elongated hollow article centrifugally cast in the mold 3 is shown at 4. The flask, mold and centrifugally cast elongated hollow article are all of annular cross section.

The common axis of all thereof is designated by the chain line 5. The internal diameter of the flask 2 is designated by the letter a and the internal diameter of the mold 3 is designated by the letter b. The internal diameter of the flask bears approximately the following relation to the internal diameter of the mold:

While I have'z described a present preferred embodiment of the invention and have explained a present preferred method of practicing the same it is to be understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

I claim:

l. A method of making a hollow mold of compacted mold forming material adapted to be rotated at high speed for the centrifugal casting of elongated hollow articles comprising selecting a hollow fiask whose internal diameter bears approximately the following relation to the internal diameter of the mold to be formed:

in which a is the internal diameter of the flask and b is the internal diameter of the mold, disposing the flask generally on end, filling the flask substantially full of uncompacted finely divided solid mold forming material, orienting the flask with its axis generally horizontal and rotating it while compacting the molding material until its density is approximately 1.4 times the density of the uncompacted mold forming material, so that the flask itself can be used to measure the quantity of uncompacted mold forming material needed for the mold and the uncompacted mold forming material is distributed along substantially the entire length of the flask during compacting thereof.

2. A method of preparing apparatus for forming hollow articles by centrifugal casting comprising providing a hollow flask adapted to have disposed therein a hollow mold of compacted nely divided solid mold forming material such that the internal diameter of the flask bears approximately the following relation to the internal diameter of the mold:

in which a is the internal diameter of the flask, b is the internal diameter of the mold and is the ratio of the specific gravity of the compacted mold forming material to the specific gravity of the uncompacted mold forming material as delivered into the flask before formation of the mold, disposing the flask generally on end, filling the flask substantially full of uncompacted mold forming material, orienting the flask with its axis generally horizontal, rotating the flask and compacting the mold forming material in the flask to form the mold until the specific gravity of the compacted mold forming material bears to the specific gravity of the uncompacted mold forming material as delivered into the flask before formation of the mold the ratio whereby the quantity of uncompacted mold iemingamgrgmaemplgygd to: me emanen er the. mold, is to ubtantially ,l'l asfk, Number so. that theask itself- .aanY berused to meaurefthe 896,194 mod 'fp zmng material, and the uncmlaied 1,474,331 :mldY formingymaifraril is 'dis-.tributed along lsulu- `l5 2,340,262 stamialy-thefentire-lengizhaf the flask. 2,449,900

LQYAL L. JOHNSTON.

Number REF.El IafNE.SV CITED 1.0 566,339 l13112.ifllonvslmg references are of -recond in the 06,534 88,2 o

@de patenti 8 UNITED .STATES BATENJfs Date I Name Bensng Aug. 18,"1908 Barks'chat Nav. 2G, 1923 Crawford Jan. S25, 1944 Johnston Sept. 21, 1948 FOREIGN PATENTS Country Darte GlealBIS/ n Q- DSQ. 22, 1944 n Great Britain Aug. 1.6., 1948 France May 12J 1930 

